SUO 2017: Advanced Imaging in Prostate Cancer: [18F] FACBC

Washington, DC (UroToday.com) Dr. Nieh from Emory University presented an excellent overview of a new PET radiotracer [18F] FACBC, generically known as fluciclovine (Axumin®). FACBC is an amino acid derivative radiotracer that was originally used in brain studies. Due to limited renal excretion, it was studied as an imaging exam for kidney cancer. However, its utility in metastatic prostate cancer (PC) was quickly realized.

Early clinical studies of FACBC showed very high sensitivity in patients at risk for PC recurrence, and in-vitro studies demonstrated higher FACBC pickup by tumor cells as compared to FDG, choline, and other common radiotracers. Imaging with FACBC is a bit different than with most other PET scans, since the greatest uptake is in the pancreas and liver, rather than urinary tract. The limited bladder involvement is very helpful for pelvic visualization, however.

To establish the clinical utility of FACBC, a study was conducted with 93 patients to compare FACBC to ProstaScint. With a median PSA of 4.0, 82% of scans were positive on whole body imaging, and 39% of patients were diagnosed with a PSA <1. This sensitivity at low PSAs is similar to results seen from choline-PET imaging. Interestingly, the sensitivity of FACBC was 5x higher for extraprostatic disease than ProstaScint, and also had excellent prostate uptake.

A subsequent multisite study with 596 patients showed that 41% of patients who had detection of recurrence had a PSA <0.79. Overall, FACBC demonstrated a 92% PPV for recurrence, which is quite dramatic. These studies led to FDA approval in May 2016 of Axumin for suspected PC recurrence.

There are several distinct advantages to using FACBC. The study is fast (20-30min) vs. the usual ~3hr bone scan, which makes for a far better patient experience. Although false positives due to inflammation are still possible, they are less likely than with FDG-PET. In a head-to-head study against 11C-choline, FACBC outperformed 11C-choline on nearly every statistical parameter (higher sensitivity, specificity, PPV, and NPV). Furthermore, it was more sensitive/specific at every PSA level, indicating an overall better imaging value. Lastly, FACBC has a much longer half-life than 11C-choline, hence it does not require an institution to have an on-site cyclotron. Instead, FACBC can be synthesized at a central facility and distributed nationally, improving the economic viability of the tracer.

There are several ongoing studies with FACBC, including comparisons with mpMRI for prostatic bed and local recurrences following treatment for PC. One of the most exciting future uses would be for helping guide which high-risk PC patients would benefit from curative-intent therapy by providing a better initial staging exam. As radical treatment for high-risk patients continues to gain popularity, this imaging test may provide unique clinical utility. While there are many tracers currently under active investigation, FACBC appears to be leading the pack with high clinical utility and impressive test characteristics.

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